1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and devices and, more particularly, to mechanisms and techniques for increasing a pressure applied to a ram blowout preventer (BOP) for sealing a wellbore.
2. Discussion of the Background
One apparatus for sealing a well is the ram BOP. The ram BOP (herein simply BOP) is a safety mechanism that is used at a wellhead of an oil or gas well. The BOP may be used for offshore drilling and also for land-based drilling. The BOP is configured to shut the flow from the well when certain events occur. One such event may be the uncontrolled flow of gas, oil or other well fluids (e.g., mud) from an underground formation into the well. Such event is sometimes referred to as a “kick” or a “blowout” and may occur when formation pressure exceeds the pressure generated by the column of drilling fluid. This event is unforeseeable and if no measures are taken to prevent and/or control it, the well and/or the associated equipment may be damaged.
The BOP may be installed on top of the well to seal the well in case that one of the above events is threatening the integrity of the well. The BOP is conventionally configured to prevent the release of pressure either in the annular space between the casing and the drill pipe or in the open hole (i.e., hole with no drill pipe) during drilling or completion operations.
In this regard, the BOP has two ram blocks that are configured to move towards each other or away from each other as desired by the operator of the rig. The operator of the rig controls the closing and opening of the ram blocks by activating various valves that control a hydraulic fluid. The hydraulic fluid is either provided from accumulators provided next to the BOP (e.g., undersea for an undersea BOP) or through pipes from the surface. By allowing the hydraulic fluid under pressure to enter a closing chamber the ram blocks are closed and by allowing the hydraulic fluid to enter an opening chamber the ram blocks are opened.
The ram blocks have at their frontal faces an elastomeric material, a packer, that has a semi-spherical profile. Thus, when the drill line is still inside (i.e., crossing the BOP) and there is a need to close the well, the ram blocks close around the drill line and the profile of the packers ensure that an interface between the drill line and the ram blocks is sealed. It is noted that shearing ram blocks have cutting edges instead of packers and when there is a need to close the BOP, the shearing ram blocks will close the well by severing the drill line.
However, in practice it is noted that sometimes the interface between the packers and the drill line is not completely sealed, i.e., there is a leakage of mud or other fluids that are present in the well. The leak is more serious as the diameter of the drill line increases. Thus, there is a need in the industry to provide a better sealing when a ram block with a packer is used to close a well while a tool is still inside the BOP.
Accordingly, it would be desirable to provide systems and methods that achieve the sealing of the well irrespective of the diameter of the drill line and to avoid the above noted shortcomings.